Chemical vapor deposition (CVD) is a known technique for forming coatings of metals and metal compounds on a variety of substrates; it has been used, for example, in the production of tantalum and tungsten coatings on steels, silica coating on silicon, and titanium carbide and nitride coating on cemented carbide tools. The technique essentially comprises contacting the substrate to be coated with the vapor of a compound of the coating metal and, where a metal compound coating is to be formed which cannot be obtained by decomposition of the vaporised coating metal compound, a vaporised or gaseous compound which contains the additional element(s) required for the desired metal compound coating and where it is required to reduce the coating metal compound and/or the additional element(s)-containing compound, hydrogen, while maintaining the substrate at a temperature at which decomposition or reaction of the compound(s) takes place with formation of the desired coating. The use of CVD to form metal and metal compound coatings on razor blade cutting edges is described in British Specification No. 1,416,887; this specification gives examples of a number of different coatings and the compounds which can be used to form them and the disclosure of this specification is incorporated herein by reference.
CVD is carried out in a suitable deposition chamber at an elevated temperature and usually at a reduced pressure (as required or desirable in order to vaporise the compound(s) used). The deposition chamber may form part of a closed system with the means for supplying the vaporised metal compound or a flow system may be used in which fresh vaporised metal compound is supplied to the deposition chamber and decomposition or reaction products are removed therefrom. The latter type of system is usually preferred because it is more versatile, easier to operate and permits a greater degree of control to be maintained over the deposition parameters.